renderthread.cpp Example File

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  #include "renderthread.h"

  #include <QtWidgets>
  #include <cmath>

  RenderThread::RenderThread(QObject *parent)
      : QThread(parent)
  {
      restart = false;
      abort = false;

      for (int i = 0; i < ColormapSize; ++i)
          colormap[i] = rgbFromWaveLength(380.0 + (i * 400.0 / ColormapSize));
  }

  RenderThread::~RenderThread()
  {
      mutex.lock();
      abort = true;
      condition.wakeOne();
      mutex.unlock();

      wait();
  }

  void RenderThread::render(double centerX, double centerY, double scaleFactor,
                            QSize resultSize)
  {
      QMutexLocker locker(&mutex);

      this->centerX = centerX;
      this->centerY = centerY;
      this->scaleFactor = scaleFactor;
      this->resultSize = resultSize;

      if (!isRunning()) {
          start(LowPriority);
      } else {
          restart = true;
          condition.wakeOne();
      }
  }

  void RenderThread::run()
  {
      forever {
          mutex.lock();
          QSize resultSize = this->resultSize;
          double scaleFactor = this->scaleFactor;
          double centerX = this->centerX;
          double centerY = this->centerY;
          mutex.unlock();

          int halfWidth = resultSize.width() / 2;
          int halfHeight = resultSize.height() / 2;
          QImage image(resultSize, QImage::Format_RGB32);

          const int NumPasses = 8;
          int pass = 0;
          while (pass < NumPasses) {
              const int MaxIterations = (1 << (2 * pass + 6)) + 32;
              const int Limit = 4;
              bool allBlack = true;

              for (int y = -halfHeight; y < halfHeight; ++y) {
                  if (restart)
                      break;
                  if (abort)
                      return;

                  uint *scanLine =
                          reinterpret_cast<uint *>(image.scanLine(y + halfHeight));
                  double ay = centerY + (y * scaleFactor);

                  for (int x = -halfWidth; x < halfWidth; ++x) {
                      double ax = centerX + (x * scaleFactor);
                      double a1 = ax;
                      double b1 = ay;
                      int numIterations = 0;

                      do {
                          ++numIterations;
                          double a2 = (a1 * a1) - (b1 * b1) + ax;
                          double b2 = (2 * a1 * b1) + ay;
                          if ((a2 * a2) + (b2 * b2) > Limit)
                              break;

                          ++numIterations;
                          a1 = (a2 * a2) - (b2 * b2) + ax;
                          b1 = (2 * a2 * b2) + ay;
                          if ((a1 * a1) + (b1 * b1) > Limit)
                              break;
                      } while (numIterations < MaxIterations);

                      if (numIterations < MaxIterations) {
                          *scanLine++ = colormap[numIterations % ColormapSize];
                          allBlack = false;
                      } else {
                          *scanLine++ = qRgb(0, 0, 0);
                      }
                  }
              }

              if (allBlack && pass == 0) {
                  pass = 4;
              } else {
                  if (!restart)
                      emit renderedImage(image, scaleFactor);
                  ++pass;
              }
          }

          mutex.lock();
          if (!restart)
              condition.wait(&mutex);
          restart = false;
          mutex.unlock();
      }
  }

  uint RenderThread::rgbFromWaveLength(double wave)
  {
      double r = 0.0;
      double g = 0.0;
      double b = 0.0;

      if (wave >= 380.0 && wave <= 440.0) {
          r = -1.0 * (wave - 440.0) / (440.0 - 380.0);
          b = 1.0;
      } else if (wave >= 440.0 && wave <= 490.0) {
          g = (wave - 440.0) / (490.0 - 440.0);
          b = 1.0;
      } else if (wave >= 490.0 && wave <= 510.0) {
          g = 1.0;
          b = -1.0 * (wave - 510.0) / (510.0 - 490.0);
      } else if (wave >= 510.0 && wave <= 580.0) {
          r = (wave - 510.0) / (580.0 - 510.0);
          g = 1.0;
      } else if (wave >= 580.0 && wave <= 645.0) {
          r = 1.0;
          g = -1.0 * (wave - 645.0) / (645.0 - 580.0);
      } else if (wave >= 645.0 && wave <= 780.0) {
          r = 1.0;
      }

      double s = 1.0;
      if (wave > 700.0)
          s = 0.3 + 0.7 * (780.0 - wave) / (780.0 - 700.0);
      else if (wave <  420.0)
          s = 0.3 + 0.7 * (wave - 380.0) / (420.0 - 380.0);

      r = std::pow(r * s, 0.8);
      g = std::pow(g * s, 0.8);
      b = std::pow(b * s, 0.8);
      return qRgb(int(r * 255), int(g * 255), int(b * 255));
  }